FERTILITY IN ANIMALS 563 



Conclusion. We may conclude, therefore, fairly, that fertility in 

 animals is a complex character highly modifiable under different con- 

 ditions of environment, but nevertheless possessing a definite, although 

 intricate and obscure, factorial basis. The character bears the same 

 relation to systems of breeding as do any other characters, that is, the 

 system of breeding in itself has no effect upon it, it is merely a mode of 

 achieving certain results. This is clearly established by Pearl's experi- 

 ments on fecundity in fowls, for they demonstrate that factors for high 

 fecundity exist, and that these factors behave like other Mendelian 

 factors. 



